While driving long distances, drivers must remain focused for lengthy periods of time and can easily become very tired or even fall asleep. During early stages of drowsiness, the driver may fall asleep for brief moments. Attention lapses and reduced alertness occur for short periods (less than 30 seconds) but the driver usually awakens with an awareness of danger. However, the driver subsequently feels weary, and continues to drift in and out of consciousness until finally falling completely asleep. In addition, persons working under highly dangerous conditions in quiet environments, e.g., analysts dealing with dangerous materials requiring focused attention, are likely to become lethargic in a short time. People who become drowsy while working under such conditions may easily lose awareness of the dangers in their surroundings.
U.S. Pat. No. 7,088,250 discloses a fatigue-level estimation apparatus to determine a fatigue level of a driver. U.S. Pat. No. 6,070,098 utilizes an observation of activities related to fatigue and determines a level of fatigue based on a large amount of processed data. However, the detected data of a drowsy driver, such as observations of a driver's behavior or the reflectivity of the eyelid, may be similar to those of an alert subject. Therefore, there is a need to reduce required data processing amount and to detect drowsiness effectively, so as to meet industrial requirements.